Conventionally, switching devices (for example MOSFETs (Metal-Oxide Semiconductor Field-Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors)) are used in various technological fields. Power modules using such devices often adopt a resin sealing structure for the purposes of enhancing reliability of electronic parts and enhancing production properties of the module. In the power module of the resin sealing structure as just-mentioned, in order to enhance radiation of the heat generated from the switching device, the switching device and a die pad on which the switching device is mounted are covered with a resin, with a heat release layer on the back side of the die pad left exposed. In addition, the exposed back side and an external cooling module are put in surface contact with each other through an insulating resin sheet therebetween. This makes it possible to secure a heat release route for releasing the heat generated by the switching device inside the module to the exterior, thereby promising an enhanced cooling efficiency for the switching device.
In recent years, the quantities of heat generated by power modules have been increasing, as the power modules have been enhanced in the degree of multifunctionality, output, and mounting density. Where the above-mentioned resin sealing structure capable of securing a heat release route while maintaining reliability is adopted, however, the heat generated by the switching devices can be diffused through the heat release layer, and can be efficiently released to the cooling module through a wide area.
Patent Document 1 discloses a power module in which a heat spreader on which a semiconductor chip is mounted and a heat sink member are joined to each other through a resin sheet having a high thermal conductivity.
Besides, Patent Document 2 discloses a printed circuit metallic substrate in which an Al layer is formed at least on one side of a Cu clad invar plate, and an insulating layer is formed thereon, whereby adhesion strength between the Cu clad invar plate and the insulating layer is enhanced.    Patent Document 1    JP-2008-101227-A    Patent Document 2    JP-61-295692-A